Ultrasonic motor and lens apparatus including the same

ABSTRACT

Provided is an ultrasonic motor, comprising: a vibrator including a piezoelectric element and a contact surface to be brought into contact with a member to be driven, the vibrator driving the member to be driven by an ultrasonic vibration excited by the piezoelectric element; a holding part configured to hold the vibrator; a pressurization unit configured to apply a bias force for biasing the holding part toward the member to be driven so as to impress the contact surface against the member to be driven; and a fixing unit configured to support the pressurization unit, in which the holding part holds the vibrator on both sides of the contact surface in a driving direction of the member to be driven.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ultrasonic motor for driving amember to be driven by generating an ellipsoidal vibration on animpressed vibrator, and to a lens apparatus using the ultrasonic motor.

2. Description of the Related Art

An ultrasonic motor has been conventionally used as a driving source fordriving, for example, a lens mechanism or a camera, taking advantage ofsilent operation, driving capability from low speed to high speed, andhigh torque output. For example, an ultrasonic motor disclosed inJapanese Patent Application Laid-Open No. 2006-158052 includes anannular member to be driven having a rotation axis, and multiplevibrators. Each vibrator is in a so-called pressurized contact conditionwith respect to the member to be driven, i.e., the vibrator is incontact with the member to be driven in a state of being impressedagainst the member to be driven. The vibrators are arranged on theannular member to be driven at predetermined intervals. When anultrasonic vibration is excited on the vibrator under the pressurizedcontact condition, an ellipsoidal motion is generated on the vibrator ata portion in contact with the member to be driven, so that the member tobe driven is driven to rotate about the rotation axis of the member tobe driven. The pressurized contact condition of the vibrator withrespect to the member to be driven is obtained by biasing, with use of aplate spring, a portion of the vibrator corresponding to a vibrationnode set near the center of the vibrator. An impressing force of theplate spring is adjusted by a screw and an adjustment washer providednear a fixing portion of the plate spring.

However, in the ultrasonic motor disclosed in Japanese PatentApplication Laid-Open No. 2006-158052, in order to prevent theultrasonic vibration excited on the vibrator from being interrupted, thevibration node needs to be set at the portion where the vibrator isimpressed. In addition, in order to obtain an appropriate pressurizedcontact condition at contact surfaces between the vibrator and themember to be driven, it is necessary to impress the vibrator against themember to be driven at the center between the contact surfaces, andtherefore the vibration node needs to be set near the center between thecontact surfaces where the vibrator is impressed, resulting in a problemthat a degree of freedom in design for the vibration is restricted.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and in an ultrasonic motor for driving a member to be drivenby an ultrasonic vibration generated on a vibrator, the degree offreedom in design for the vibration is improved while securing anappropriate pressurized contact condition at a contact surface betweenthe vibrator and the member to be driven.

According to the present invention, provided is an ultrasonic motor,comprising: a vibrator including a piezoelectric element and a contactsurface to be brought into contact with a member to be driven, thevibrator driving the member to be driven by an ultrasonic vibrationexcited by the piezoelectric element; a holding part configured to holdthe vibrator; a pressurization unit configured to apply a bias force forbiasing the holding part toward the member to be driven so as to impressthe contact surface against the member to be driven; and a fixing unitconfigured to support the pressurization unit, in which the holding partholds the vibrator on both sides of the contact surface in a drivingdirection of the member to be driven.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an ultrasonic motor accordingto a first embodiment of the present invention.

FIG. 2 is a perspective view for illustrating an assembled state ofmembers illustrated in FIG. 1.

FIG. 3 is an enlarged perspective view for illustrating a joined stateof a vibrator and a smaller base.

FIG. 4A is an enlarged cross-sectional view for illustrating theassembled state of the members according to the first embodiment.

FIG. 4B is an enlarged cross-sectional view for illustrating theassembled state of the members according to the first embodiment.

FIG. 4C is an enlarged detail view of a portion A illustrated in FIG.4B, for illustrating component vectors of an impressing force of anelastic member.

FIG. 5 is an enlarged cross-sectional view for illustrating a state inwhich a rotor and a ring base are respectively inclined.

FIG. 6A is an enlarged cross-sectional view for illustrating anassembled state of members according to a second embodiment of thepresent invention.

FIG. 6B is an enlarged cross-sectional view for illustrating theassembled state of the members according to the second embodiment.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will be described indetail in accordance with the accompanying drawings.

First Embodiment

Exemplary embodiments of the present invention are described below withreference to the accompanying drawings. Although a rotary driving typemotor that is formed in a unit as an actuator for driving a lens barrelor the like for a digital camera is described as an example of anultrasonic motor according to this embodiment, its usage is not limitedto this.

FIG. 1 is an exploded perspective view of an ultrasonic motor accordingto a first embodiment of the present invention. In the figures, the samemembers are represented by the same reference symbols. As illustrated inFIG. 1, the ultrasonic motor according to the first embodiment includesa rotor 101, a vibration plate 102, a piezoelectric element 103, asmaller base 104, a ring base 105, a pressurization member 106 and aplate spring 107. The rotor 101 is a member to be driven, including acontact surface 101 a with which a vibrator 109 described later comesinto pressurized contact by an impressing force. The vibration plate 102is a member in contact with the contact surface 101 a under apressurized contact condition involving an impression. The piezoelectricelement 103 is tightly adhered to the vibration plate 102 with anadhesive or the like. When a voltage is applied to the piezoelectricelement 103 in a state in which the piezoelectric element 103 is tightlyadhered to the vibration plate 102, an ellipsoidal motion can begenerated. The vibration plate 102 and the piezoelectric element 103constitute the vibrator 109. In this embodiment, the vibrator 109 isprovided at three points, thus driving the rotor 101 to rotate. Thesmaller base 104 is a holding member for holding the vibrator 109. Thering base 105 is a fixing member for holding the smaller base 104, andthe pressurization member 106 and plate spring 107. The pressurizationmember 106 is fitted into a through hole part 105 b of the ring base105, and is held to move only in a direction perpendicular to thecontact surface 101 a of the rotor 101, thus causing the vibrator 109 tocome into pressurized contact with the rotor 101 via the smaller base104 by an impressing force from the plate spring 107 described later.The plate spring 107 serves as an elastic member, which is fixed to thering base 105 with a screw 108 at each end portion thereof, and causesthe vibrator to come into pressurized contact with the member to bedriven by an impressing force of the plate spring. The pressurizationmember 106 and the plate spring 107 constitute a pressurization unit ofthe present invention.

As described above, the above-mentioned members are assembled in a unitas an ultrasonic motor.

FIG. 2 is a perspective view for illustrating an assembled state of themembers illustrated in FIG. 1. In FIG. 2, a configuration around thevibrator 109 is the same for all three points, and hence, to simplifythe figure, the reference symbols are assigned only to a front side inthe figure. As illustrated in FIG. 2, at each of the three points of thering base 105, an impressing force is applied to the vibrator 109 by theplate spring 107 that is fixed with the two screws 108 via thepressurization member 106 and the smaller base 104, and as a result, thevibrator 109 and the contact surface 101 a of the rotor 101 come intopressurized contact with each other. When actually mounting theultrasonic motor on the lens barrel or the like, the rotor 101 iscoupled to a focusing mechanism or a zoom mechanism for driving.

Hereinafter, details on the structural members of the ultrasonic motorare described. FIG. 3 is an enlarged perspective view for illustrating ajunction status of the vibration plate 102 and the smaller base 104illustrated in FIGS. 1 and 2 as viewed from the rotor 101 side. Asillustrated in FIG. 3, two projection parts 102 b are formed on a platepart 102 a at the center of the vibration plate 102. Upper end surfacesof the projection parts 102 b, i.e., surfaces coming into abutment onthe contact surface 101 a of the rotor 101, are formed on the sameplane, and in order to obtain an appropriate abutment condition withrespect to the contact surface, the upper end surfaces are finished assmooth surfaces by polishing or the like in a manufacturing process.

On the other hand, the piezoelectric element 103 is tightly adhered to aback surface side of the plate part 102 a illustrated in FIG. 3 (asurface side opposite to the surface on which the two projection parts102 b are formed) with an adhesive or the like. The method of tightlyadhering the piezoelectric element 103 to the back surface side of theplate part 102 a is not limited as long as the two components aretightly adhered to each other. The piezoelectric element 103 includesmultiple piezoelectric element films laminated and integrated. Anapplication of a desired alternate-current (AC) voltage to thepiezoelectric element 103 formed by laminating the multiplepiezoelectric element films causes a vibration, thus exciting twovibration modes on the vibration plate 102 having the piezoelectricelement 103 tightly adhered thereto. At this time, by setting vibrationphases of the two vibration modes to obtain a desired phase difference,an ellipsoidal motion is generated on the projection parts 102 b asindicated by arrows illustrated in FIG. 3. The ellipsoidal motion isgenerated on the vibrator 109 at the three points as illustrated inFIGS. 1 and 2 and transferred to the contact surface 101 a of the rotor101, so that the rotor 101 can be driven to rotate. Details on theabove-mentioned laminated structure of the piezoelectric element and theabove-mentioned vibration mode are substantially the same as thecontents described in Japanese Patent Application Laid-Open No.2004-304887. The entire content of Japanese Patent Application Laid-OpenNo. 2004-304887 is hereby incorporated by reference as if presentedherein in its entirety.

Two junction parts 102 c for joining to higher upper surface parts 104 aformed on both sides of the smaller base 104 are formed on both ends ofthe vibration plate 102. Although the vibration plate 102 is joined tothe smaller base 104 by welding or adhering at the junction part 102 c,the method of joining the vibration plate 102 and the smaller base 104is not limited as long as the vibration plate 102 and the smaller base104 are joined to each other. Two arm parts (connection parts) 102 d areformed respectively between the two junction parts 102 c and the platepart 102 a, and the vibration plate 102 and the piezoelectric element103 are fixed to the smaller base 104 via the arm parts 102 d. The armparts 102 d are formed into a narrower shape than the plate part 102 aand the junction part 102 c as illustrated in FIG. 3 to achieve such aconfiguration that hardly transfers the vibration generated on the platepart 102 a to the junction part 102 c, i.e., a configuration having ahigh vibration damping rate. In other words, a coupling configurationfor preventing the vibration generated on the plate part 102 a frombeing interrupted by the smaller base 104 that is a rigid member isachieved by the junction parts 102 c. In addition, a predetermined space203 is formed between a flat portion 104 b near the center of thesmaller base 104 and a surface (not shown) of the piezoelectric element103 facing the flat portion 104 b.

In the ultrasonic motor that is driven by a frictional force between thecontact surfaces of the vibrator 109 and the rotor 101, in order tosecure an appropriate contact condition, it is important to impress thecenter of the plate part 102 a and reduce an uneven impression. In orderto impress the center of the plate part 102 a, it is required to impressthe center of the vibrator 109. In the ultrasonic motor disclosed inJapanese Patent Application Laid-Open No. 2006-158052, the vibrator isimpressed in a direct manner. For this reason, in order to prevent theultrasonic vibration excited on the vibrator 109 from being interrupted,it is necessary to set a vibration node to the center of the vibrator109. Therefore, when generating an ellipsoidal motion on the projectionparts 102 b by combining the two vibration modes, it is necessary to setthe vibration node to the center of the vibrator 109 for each of thevibration modes. As a result, a problem occurs in that a degree offreedom in design for the vibration is restricted.

However, in the ultrasonic motor according to the present invention, thevibrator 109 is held by the smaller base 104 via the arm parts 102 d forsuppressing a transfer of the vibration, and hence it is not necessaryto set the vibration node to the center of the vibrator 109. Therefore,as disclosed in Japanese Patent Application Laid-Open No. 2004-304887,for example, the two vibration modes can be set in such a manner that anode of one of the vibration modes does not exist at the center of thevibrator 109. As a result, an ultrasonic motor having a high degree offreedom in design for the vibration can be achieved.

In the ultrasonic motor according to the present invention, the armparts 102 d are provided on outer sides of the projection parts 102 b inthe driving direction. In addition, the junction parts 102 c areprovided on outer sides of the arm parts 102 d in the driving direction.As a result, it is possible to reduce a size in a directionperpendicular to the driving direction, i.e., a radial direction of therotor. Therefore, downsizing of the ultrasonic motor can be achieved bythe present invention.

FIGS. 4A and 4B are enlarged cross-sectional views for illustrating theassembled state of the members, in which only a surrounding area of oneof the three vibrators 109 illustrated in FIG. 2 is illustrated in anenlarged manner. The rest of two vibrators have the same configuration,and a description thereof is omitted.

FIG. 4A is a view in which the rotor 101 is located on the upper side,having a cutting plane on a plane including respective centers ofgravity of the upper end surfaces coming into contact with the contactsurface 101 a of the rotor 101 in the two projection parts 102 b of thevibration plate 102 and respective normals of the upper end surfacesoriginated at the respective centers of gravity.

FIG. 4B illustrates a cutting plane on a plane including a center ofgravity of the whole upper end surface coming into contact with thecontact surface 101 a in the projection parts 102 b of the vibrationplate 102 illustrated in FIG. 3 and a normal of the contact surface 101a, and perpendicular to the view illustrated in FIG. 4A. The whole upperend surface refers to a surface including all the two upper endsurfaces.

In FIGS. 4A and 4B, a center line 201 is a line passing through thecenter of gravity of the whole upper end surface coming into contactwith the contact surface 101 a in the projection parts 102 b of thevibration plate 102 and including the normal of the contact surface 101a.

The upper end surfaces of the projection parts 102 b abut on the contactsurface 101 a of the rotor 101, and are held in a pressurized contactcondition. In addition, the junction parts 102 c on both ends of thevibration plate 102 are joined to the smaller base 104 at the two uppersurface parts 104 a. The predetermined space 203 is then formed betweenthe piezoelectric element 103 and the flat portion 104 b of the smallerbase 104.

A hole part 104 c and an elongated hole part 104 d are provided on thelower surface side of the smaller base 104, and two shaft parts 105 aformed on the ring base 105 are respectively fitted therein. An abuttingpart 104 e is provided on the lower center of the smaller base 104. Theabutting part 104 e is formed into a half cylindrical shape in which anarc shape illustrated in FIG. 4A extends in a direction of the depth ofthe drawing sheet (a lateral direction in FIG. 4B). An upper end surface106 a of the pressurization member 106 comes into contact with theabutting part 104 e. The upper end surface 106 a is formed as a flatsurface, and hence the contact with the abutting part 104 e is a linecontact having a length in the direction of the depth of the drawingsheet in FIG. 4A (the lateral direction in FIG. 4B). Although theabutting part 104 e is formed into the half cylindrical shape having thearc shape as described above in the first embodiment, the shape of theabutting part 104 e is not limited as long as the abutting part 104 eand the upper end surface 106 a of the pressurization member 106 canmaintain the line contact of a straight line.

The ring base 105 includes the through hole part 105 b on a surfacefacing the plate spring 107 as illustrated in FIG. 1, and thepressurization member 106 comes into contact with the plate spring 107by being fitted in the through hole part 105 b, thus cooperating withthe plate spring 107. The center axes of the through hole part 105 b andthe pressurization member 106 substantially match the center line 201,i.e., an axial direction perpendicular to the contact surface 101 a. Theplate spring 107 is deformed to come into contact with a sphericalsurface part 106 b on the lower side of the pressurization member 106 inFIGS. 4A and 4B in a state in which the pressurization member 106 isbiased against the smaller base 104 by an elastic force of the platespring 107.

The plate spring 107 needs to have a reduced spring constant to someextent in order to reduce a fluctuation of the impressing force due to achange of a deformation amount. Therefore, it is desired that the platespring 107 be as thin as possible and the plate spring 107 be as long aspossible. The plate spring 107 according to the first embodiment isformed with use of a thin plate into an arc shape in order to achieve aslarge a spring length as possible in the annular ultrasonic motor. Withthis structure, the fluctuation of the bias force by the plate spring107 can be suppressed even when a displace amount of the pressurizationmember 106 in the impressing direction is changed to some extent.Therefore, unlike a conventional example, a mechanism for adjusting theimpressing force is not necessary. With the above-mentionedconfiguration, the vibrator 109 is impressed against the rotor 101 bythe plate spring 107 via the smaller base 104 and the pressurizationmember 106.

A configuration for transferring the impressing force by the platespring 107 is described below with reference to FIGS. 4A, 4B and 4C. Inthe following description, an impressing force vector is a force vectorincluding a direction and a magnitude of the impressing force in thecross section of each figure.

As illustrated in FIG. 4A, the smaller base 104 is held in contact withthe pressurization member 106 at the abutting part 104 e. The smallerbase 104 is further held in contact with the rotor 101 at the twoprojection parts 102 b, and the center of gravity of each contactsurface is located at the same distance from the center line 201 in thedriving direction of the rotor. On the other hand, regarding the contactbetween the plate spring 107 and the pressurization member 106, theplate spring is formed into an arc shape in the first embodiment, andhence, the support parts on both ends of the plate spring 107 and aninput point of the impressing force (a contact point between the platespring 107 and the pressurization member 106) do not exist on a straightline. Therefore, a cross section of the plate spring when generating theimpressing force is in a state having an inclination as illustrated inFIG. 4B. As a result, the impressing force vector input to thepressurization member 106 by the plate spring 107 can be indicated by anarrow 206 a. The contact point between the pressurization member 106 andthe plate spring 107 does not exist on the center line 201, and in FIG.4B, the contact point is shifted to a point 205 on the right side of thecenter line 201.

FIG. 4C is an enlarged detail view of a vicinity of the point 205 in aportion A illustrated in FIG. 4B. The impressing force applied to thepressurization member 106 by the plate spring 107 is represented by thevector 206 a, which is inclined with respect to the center line 201.Therefore, the impressing force vector 206 a can be divided into acomponent vector 206 b in a direction parallel to the center line 201and a component vector 206 c in a direction perpendicular to the centerline 201.

The pressurization member 106 is held by the ring base 105 with a degreeof freedom only in a direction substantially parallel to the center line201 as illustrated in FIGS. 4A and 4B, and hence, the impressing forcevector 206 a applied to the pressurization member 106 by the platespring 107 is transferred to the smaller base 104 with a force (vector204 a) corresponding to the component vector 206 b in the direction ofthe center line 201.

On the other hand, the impressing force (vector 204 a) transferred tothe smaller base 104 is transferred to the contact surface 101 a by thetwo projection parts 102 b, and a force of impressing the contactsurface 101 a by each of the projection parts 102 b is a half (vector204 b) of the impressing force vector 204 a. Therefore, the impressingforces on the two projection parts 102 b can be evenly maintained.

The contact between the projection parts 102 b and the contact surface101 a is a surface contact, and hence, in practice, the impressing forceis evenly distributed on the plane. However, for the sake of betterunderstanding, the impressing force is represented as a force vectoracting on a position of the center of gravity of the plane. Likewise,the contact between the pressurization member 106 and the abutting part104 e of the smaller base 104 is a line contact, and hence, in practice,the impressing force vector is evenly distributed on the line. However,the impressing force vector is also represented as a force vector actingon a position of the center of gravity of the line. Hereinafter, theimpressing force is represented as a force vector at the position of thecenter of gravity for both the surface contact and the line contact.

In addition, on a side surface part of the pressurization member 106, africtional force is generated by the component vector 206 c of theimpressing force vector 206 a input to the pressurization member 106 bythe plate spring 107, the component vector 206 c acting in the directionperpendicular to the center line 201. On the other hand, a frictionalforce is also generated on the fitting portions of the shaft parts 105a. These frictional forces are ignored because these are sufficientlysmall with respect to the impressing force. In practice, if thefinishing of the side surface is smoothened to some extent, an influenceof the frictional forces can be reduced to a level that can be ignored.

In the first embodiment, as described above, the pressurization member106 is substantially held on the ring base 105 in a state of having adegree of freedom only in the direction of the center line 201.Therefore, the impressing force vector 204 a applied to the smaller base104 by the pressurization member 106 can be substantially matched withthe center line 201. At this time, the magnitude of the impressing forcevector 204 a is equal to the component vector 206 b of the impressingforce vector 206 a by the plate spring in the direction parallel to thecenter line 201. This is because only the component vector 206 b of theimpressing force vector 206 a works as the impressing force vector 204a. The component vector 206 c of the impressing force vector 206 a inthe direction perpendicular to the center line 201 affects thefrictional force on the side surface part of the pressurization member106. Through the smooth finishing of the surfaces, the frictional forcegenerated between the side surface of the pressurization member 106 andan internal surface of the through hole part 105 b is sufficiently smallcompared to the impressing force, and does not interfere with a smoothreciprocating movement of the pressurization member 106. Finally, theimpressing force vector applied to the contact surface 101 a by one ofthe projection parts 102 b is the impressing force vector 204 b, and itsmagnitude is a half of the impressing force vector 204 a. This isbecause the projection parts 102 b exist at two points as illustrated inFIG. 4A. In this manner, referring to the cross sections illustrated inFIGS. 4A and 4B, the point of load of the input impressing force vector206 a is shifted from the center line 201, and the direction of theimpressing force vector 206 a is not parallel to the center line 201,but the impressing force vectors 204 a and 204 b can maintain anappropriate impressing force.

On the other hand, the smaller base 104 is impressed via a line-shapedcontact part of the abutting part 104 e. Therefore, in the cross sectionillustrated in FIG. 4A, the smaller base 104 can be inclined and canmaintain an appropriate pressurized contact condition even wheninclination of a member occurs due to a dimension error at the time ofmanufacturing or a disturbance.

FIG. 5 is a cross-sectional view in the same cross section of the samemembers illustrated in FIG. 4A, for illustrating a case in whichrelative rotational inclination occurs about the abutting part 104 e ofthe smaller base 104 on the rotor 101 and the ring base 105 compared tothe state illustrated in FIG. 4A. Even in FIG. 5, the projection parts102 b of the vibration plate 102 follow the contact surface 101 a of therotor 101, thus maintaining an appropriate pressurized contactcondition. Although the ring base 105 is fitted into the smaller base104 by the hole part 104 c, the elongated hole part 104 d, and the shaftparts 105 a, the smaller base 104 and the ring base 105 can berelatively inclined because there is a fitting clearance, i.e., afitting space. Therefore, the contact surface 101 a can be appropriatelyimpressed at the two projection parts 102 b even when inclination of amember occurs on the rotor 101 and the ring base 105 due to a dimensionerror at the time of manufacturing or even when inclination of a memberoccurs on the rotor 101 and the ring base 105 due to a vibration or adisturbance at the time of driving.

That is, in the cross section of FIG. 4A, even when the inclination asin the case illustrated in FIG. 5 occurs between the members, such aproblem is solved by bringing the abutting part 104 e of the smallerbase 104 and the pressurization member 106 of FIG. 4A into point contactand maintaining a following capability between the contact surfaces withrespect to the inclination. On the other hand, in the cross sectionillustrated in FIG. 4B, the smaller base 104 and the pressurizationmember 106 are not inclined with respect to each other in the lateraldirection in FIG. 4B by bringing the abutting part 104 e of the smallerbase 104 and the pressurization member 106 into line contact of astraight line.

As described above, in the first embodiment, the vibrator 109 is held bythe smaller base 104 via the arm parts 102 d that suppress the transferof the vibration. Therefore, there is no restriction on the position ofthe vibration node, and hence it is possible to achieve an ultrasonicmotor with an improved degree of freedom in design for the vibrationwhile securing an appropriate pressurized contact condition at thecontact surface between the vibrator and the member to be driven.

Second Embodiment

A second embodiment of the present invention is a modification exampleof the first embodiment, in which an abutting part at which the smallerbase 104 and the pressurization member 106 come into contact with eachother has a spherical shape. FIGS. 6A and 6B are enlargedcross-sectional views for illustrating an assembled state of themembers, in which only one of the three vibrators 109 is illustrated inan enlarged manner. The direction and the position of the cutting planeillustrated in FIGS. 6A and 6B are the same as those illustrated inFIGS. 4A and 4B. With reference to FIGS. 6A and 6B, by providing anabutting part 104 f having a spherical shape on the smaller base 104,the pressurization member 106 further comes into point contact in thedirection of the depth of the drawing sheet in FIG. 6A (lateraldirection in FIG. 6B), thus enabling the inclination to be achieved inthe direction of the depth of the drawing sheet as well. Therefore, evenwhen inclination occurs on the rotor 101 and the ring base 105 in theradial direction due to a dimension error occurring at the time ofmanufacturing or even when inclination of a member occurs in thedirection of the depth of the drawing sheet in FIG. 6A (lateraldirection in FIG. 6B) due to a vibration or a disturbance at the time ofdriving, an appropriate pressurized contact condition can be maintainedon the two projection parts 102 b. Although the abutting part 104 f hasthe spherical shape as described above in the second embodiment, theshape is not limited as long as the point contact, in which the abuttingpart 104 f and the upper end surface 106 a of the pressurization member106 come into contact with each other at one point, can be maintained.

Structural elements other than the above-mentioned abutting part 104 fin the spherical shape and the method of transferring the impressingforce from the plate spring 107 are the same as those of the firstembodiment, and a description thereof is omitted.

As described above, in the second embodiment, the smaller base 104 andthe pressurization member 106 come into point contact with each other atthe abutting part 104 f having the spherical shape, and hence, even wheninclination occurs not only in the driving direction of the rotor butalso in a direction perpendicular to the driving direction of the rotor,an appropriate pressurized contact condition can be maintained.

Third Embodiment

A lens apparatus having the effect of the present invention can beachieved by employing the ultrasonic motor according to the first orsecond embodiment as a driving unit for driving a focusing lens or azoom lens in the lens apparatus.

As described above, in the ultrasonic motor for driving the member to bedriven by an ellipsoidal vibration generated on the vibrator, anappropriate pressurized contact condition at the contact surface of thevibrator and the member to be driven can be achieved without setting avibration node near the center of the contact surface where the vibratoris impressed as in the conventional technology, by improving the degreeof freedom in design for the vibration while securing the appropriatepressurized contact condition at the contact surface between thevibrator and the member to be driven.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2011-172018, filed Aug. 5, 2011, which is hereby incorporated byreference herein in its entirety.

1. An ultrasonic motor, comprising: a vibrator including a piezoelectricelement and a contact surface to be brought into contact with a memberto be driven, the vibrator driving the member to be driven by anultrasonic vibration excited by the piezoelectric element; a holdingpart configured to hold the vibrator; a pressurization unit configuredto apply a bias force for biasing the holding part toward the member tobe driven so as to impress the contact surface against the member to bedriven; and a fixing unit configured to support the pressurization unit,wherein the holding part holds the vibrator on both sides of the contactsurface in a driving direction of the member to be driven.
 2. Anultrasonic motor according to claim 1, wherein: the vibrator comprises:a plate part including a projection part forming the contact surface tobe brought into contact with the member to be driven, and thepiezoelectric element; a junction part joined to the holding partconfigured to hold the vibrator; and a connection part configured toconnect the junction part and the plate part; and the connection parthas a higher vibration damping rate than the plate part.
 3. Anultrasonic motor according to claim 2, wherein the connection part isnarrower than the plate part.
 4. An ultrasonic motor according to claim1, wherein: the pressurization unit comprises a pressurization memberand an elastic member; the elastic member applies the bias force to theholding part via the pressurization member; and the holding partcomprises an abutting part to be brought into point contact with thepressurization member, the abutting part including a normal of a planeincluding the contact surface and passing through a center of gravity ofthe contact surface.
 5. An ultrasonic motor according to claim 1,wherein: the pressurization unit comprises a pressurization member andan elastic member; the elastic member applies the bias force to theholding part via the pressurization member; and the holding partcomprises an abutting part to be brought into line contact with thepressurization member in a direction perpendicular to the drivingdirection of the member to be driven.
 6. An ultrasonic motor accordingto claim 1, further comprising a space formed between the vibrator andthe holding part.
 7. A lens apparatus, comprising the ultrasonic motoraccording to claim 1 as a driving unit configured to drive the member tobe driven.